I always loved the funeral song from Shakespeare's Cymbeline Act IV, scene 2.
Fear no more the heat o' the sun; Nor the furious winter's rages, Thou thy worldly task hast done, Home art gone, and ta'en thy wages; Golden lads and girls all must, As chimney sweepers come to dust. Fear no more the frown of the great, Thou art past the tyrant's stroke: Care no more to clothe and eat; To thee the reed is as the oak: The sceptre, learning, physic, must All follow this, and come to dust. Fear no more the lightning-flash, Nor the all-dread thunder-stone; Fear not slander, censure rash; Thou hast finished joy and moan; All lovers young, all lovers must Consign to thee, and come to dust. No exorciser harm thee! Nor no witchcraft charm thee! Ghost unlaid forbear thee! Nothing ill come near thee! Quiet consummation have; And renowned be thy grave!
Another one I can think of (and probably the most beautiful poem about death) that has always been a source of comfort for me has been Thanatopsis by William Cullen Bryant. Especially the final stanza:
So live, that when thy summons comes to join The innumerable caravan, that moves To that mysterious realm, where each shall take His chamber in the silent halls of death, Thou go not like the quarry-slave at night, Scourged to his dungeon, but, sustained and soothed By an unfaltering trust, approach thy grave, Like one who wraps the drapery of his couch About him, and lies down to pleasant dreams.